Picture-transmitting system



July 9, 1929. w s 1,719.916

PICTURE TRANSMITTING SYSTEM Filed Dec. 31, 1924 Jump. Liam flag, fist.

INVENTOR lifnlts'w/e/ AITORNEY Patented July 9, 1929, A

UNITED ,STATES 1,719,916 PATENT OFFICE.

EDWARD F. WATSON, OF LARCHMONT, NEW YORK, ASSIGNOIt TO AMERICAN TELE-PHONE ANDY'IELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

' PICTURE-TRANSMITTING SYSTEM.

Application filed December 31, 1924. Serial No. 759,098.

An object of my invention is to provide a new and improved system forsynchronizing the transmitting and receiving apparatus in a picturetransmitting system. Another obj ect of my invention is to provide forsending synchronizing currents in the same frequency range as thepicture transmitting currents.

A further object is to do this without introducing currents of excessivemagnitude that might produce objectionable inductive effects inneighboring circuits. Another object is to provide a picturetransmitting system that shall be simple and inexpensive, easy to op-.

' erate and easy to keep inorder, and free from complications in itsoperation. These and various other objects of my invention will be comeapparent on consideration of the following specification and claimstaken with the accompanying drawing in which lhave illustrated onespecific embodiment of the invention. It will be understood that thefol-- lowing specification relates more particularly to this example ofthe invention and that theinvention will be defined in the appendeclaims. I

Referring to the drawings, Figure 1 is a diagrammatic representation .ofa picture transmittingsystem embodying my invention, andFi'g. 2 is anelevation of a picture transmitting drum.

At the transmitting station at the left of Fig. 1 the picture in theform of a semi-transparent film is wrapped on the glass drum 24 which is,mounted to rotate on the shaft 26. The glass drum 24 is open at oneend, and the shaft 26 supports it at the other .end,"and inside of thedrum 24 is a photoelectric cell 25. The shaft 26 is screw-threaded inits bearings, so that as the drum 24 rotates it is traversed in slowlylongitudinally.

Light from the lamp 2l.is focused by the lens 22 on a small opening inthe screen 23 adjacent to the surface of the film on the drum 24. Thelight passes throughthis opening in the screen 23 and, through theunderlying spot of the picture film on the drum 24 to the photoelectriccell 25.

The quantity of light falling on the photoelectric cell 25 variesinaccordance with the so degree of shade of the portion of the filmunderlying the opening in the screen 23. This varies the currentaccordingly inthe circuit of the cell 25, and this current isamplifiedby the amplifier 27 and applied to modulate a 55 certaincarrier current as will be described presently. Further structuraldetails of the transmitting station will be alluded to when theoperation of the system is described a little farther along in thisspecification.

At the receiving station the light from the lamp 33 passes through anelectrically controlled light valve 34 and through an opening in thescreen 35 to the underlying spot of a sensitive film wrapped on the drum36. This drum 36 is mounted on a shaft 37 which turns in screw-threadedbearings 'of the same pitch as for the shaft 26' at the sending end. Thesensitive film on the drum 36 will have a shade produced at each spottherein corresponding to the opening of the light valve 34 at the timethat the spot underlies the opening in the screen 35.

The apparatus is shown in a condition of rest.- 'Assume that the picturefilm is in place on the drum 24 at the sending end and the sensitivereceiving film is in place on the drum 36 at the receiving end. At bothends motors such as 19 in Fig. 2 are driving continuously by means offriction clutches 20 engaging extensions of the respective shafts 26 and37. These motors are adjusted, so that the drum at the receiving endwill complete a revolution in slightly less time than at the sendingend.

To start the system in operation, the operator at the sending end closesthe switch 30 whereupon the magnet 31 retracts the hook 39 from the lug40 on the drum 24. Immediately the drum 24 starts rotating in thedirection of the arrow and the lug 41 closesthe switch B, thus sendingoscillatory 'current from the oscillator 29 into the amplifier 32 andthence over the line to the receiving end. This received current isamplified at 46, detected at 47 and applied through relay 49 to actuatemagnet 38, which retracts the hook 44 from the lug 45 on the receivingdrum 36, which thereupon begins to rotate in the direction of the arrow.I

, Very soon the lug 43 on the receiving drum 36 moves far enough toshift the switch A, thus opening the circuit to the relay 49 and closinga circuit (hitherto open) to the light valve 34.

The closure of the switch B at the sending end by the lug 41 is of shortduration, and soon after this switch opens the lug 42 permits the switchA to shift, thus closing the circuitdirect from the oscillator 29 to theinput of the modulator 28.

The current passing through the modulator 28 is modulated by the currentdetermined bythe photoelectric cell 25, so that during the period forthe rotation of the drum 24 after its start, a modulated current is sentfrom the line corresponding to the degree of shade in the successiveportions of a narrow strip of the film on drum 24 passing around underthe opening in the screen 23.

At the receiving station this modulated picture transmitting currentdetermines the ogening of the light valve 34 and therefore a ects thefilm on the drum 36 with light corresponding to the degree of shade inthe film on drum 24 at the sending end.

The switch 30 remaining closed, the drum 24 rotates continuously at thesending end. Since the drum 36 rotates a trifle faster, it is stopped ateach revolution by the hook 44 engaging the lug 45. But just before eachsuch stoppage the picture transmitting current is interrupted by' thelug 42 on the sending drum 24 shifting the switch A, thus breaking thecircuit from the oscillator 29 to the modulator 28 and making thecircuit from the oscillator 29 to the amplifier 32 except for theopening at the switch B. However, immediately after the switch A closes,the lug 41 engages the switch B and completely closes this circuit for abrief duration of time during which the current from the oscillator 29goes directly to the amplifier 32 and thence over the line and to themagnet 38 withdrawing the hook 44 and releasing the drum 36 for anotherrevolution. m

Thus it will be seen that as the drum 24 rotates, successive elementalareas of the picture film pass in helical order under the opening in thescreen 23, and in synchronism therewith successive elemental areas ofthe sensitive film on the drum 36 at the receiving end pass in helicalorder under the opening in the screen 35. I

It will be seen that the currents put on the line for the purpose ofsynchronizing are within the same frequency range and the same magnituderange as the picture transmitting currents, so that no extension of thefrequeney range is necessary beyond that for the transmission ofthepicture shades, and no excessive magnitude of current is necessarysuch as mig t produce objectionable inductive efiects in neighboringcircuits.

I claim: 1. The method of. electro-o tical transmiss1on over a wirecircuit, w ich comprises scanning a picture or object in successivelinear elements, modulating a sustained alternating carrier current inaccordance with the shade of successive points in each linear element bcontinuously varying a characteristic of t e carrier current,periodically interrupting said modulating for a brief interval betweenthe scanning of linear elements, and during said intervals transmittingunmodulated alternating carrier current from said source forsynchronizing purposes the amplitude of which is not greater than thatof the transmitted .picture modulated carrier currents.

2. In an electro-optical transmission system, a transmitting station andreceiving station, a line connecting said stations, means at saidtransmitting station for scanning an object in successive linearelements, a source of sustained alternating carrier current, means formodulating carrier current from said source in accordance'with the shadeof successive points ineach linear element by continuously varying acharacteristic of the carrier-current, and means for periodicallyinterrupting said modulating for a brief interval between the scanningof linear elements and for transmitting during said interval unmodulatedalternating carrier current from said source for, synchronizing purposesthe amplitude of which is not greater than that of the transmittedpicture modulated carrier currents.

3. An electro-optical transmission system comprising a transmittingstation and a receiving station, a line connecting said stations, a drumat the transmitting station for holding a picture an image of which isto be produced at the receiving station, a similar drum at the receivingstation for holding a sensitized film on which said image is to beproduced, means at each of said stations for moving said drums so as totraverse the points on said picture and said sensitized filmrespectively in'a helical line with respect'to a source of light, asource of sustained alternating carrier current at said transmittingstation, means for modulating carrier current from said source inaccordance with the shade of successive points on said picture bycontinuously varyinga characteristic of the carrier current, means forcontrolling the exposure of the film at the receiving station inaccordance with the characteristic of said modulated carrier current,means for periodically interrupting said modulating for a briefinterval, and means for transmitting unmoduilated alternating carriercurrent from said source during said interval for synchronizing thedrums at the transmitting and receiving stations, the amplitude of saidalternating current being not greater than that of the

